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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //发布者
        class Dep{
            constructor(){
                this.subs=[]//记录所有的订阅者
            }
            addSub(sub){
                if(sub&&sub.update){
                    this.subs.push(sub)
                }
            }
            notify(){
                this.subs.forEach(sub=>{
                    sub.update()
                })
            }
        }
        //订阅者
        class Watcher{
            update(){
                console.log('update')
            }
        }
        let dep=new Dep()
        let watcher=new Watcher()
        dep.addSub(watcher)
        dep.notify()
    </script>
</body>
</html>